According to research covering the last decade, the average number of rooms added by high-end hotel chains was lower than what the hotel industry average did for this period, but their occupancy and room rates grew faster than the average hotel.

(A) than what the hotel industry average did for this period, but their occupancy and room rates grew faster than
(B) than the hotel industry average for this period, but occupancy and room rates grew faster for these chains than for
(C) as compared to the hotel industry average for this period, but occupancy and room rates for them grew faster than with
(D) as compared to what the hotel industry average had been for this period, but occupancy and room rates for these chains grew faster than did
(E) as compared to the hotel industry average for this period, but their occupancy and room rates grew faster than they did for

For ans a the “pre-but” phrase comparison looks good but in the “post-but” comparison “their” makes no sense.

For ans b “pre-but” comparison seems false as no of rooms are getting compared with hotel industry. In “post-but” phrase the comparison is good.

What am I missing in deducing the correct OA (b)?